Diagnostic test

Command:

TestsDiagnostic test

Description

Allows to calculate test characteristics such as sensitivity, specificity, positive and negative likelihood ratio, disease prevalence as well as positive and negative predictive value, from data entered in a 2x2 table.

Required input

Enter the number of cases in the diseased group that test
positive and negative (left column); and the number of cases in the non-diseased group that test
positive and negative (right column).

Note: you can change the order of columns and rows by clicking the button.

Disease prevalence

If the sample sizes in the positive (Disease present) and the negative (Disease absent) groups do not reflect the real prevalence of the disease, you can enter the disease prevalence in the corresponding input box. This will have an effect on the positive and negative predictive values.

Results

The following statistics are reported with their 95% Confidence intervals:

Sensitivity: probability that a test result will be positive when the disease is present (true positive rate).

Specificity: probability that a test result will be negative when the disease is not present (true negative rate).

AUC: Area under the ROC curve.

Positive likelihood ratio: ratio between the probability of a positive test result given the presence of the disease and the probability of a positive test result given the absence of the disease, i.e.
= True positive rate / False positive rate = Sensitivity / (1-Specificity)

Negative likelihood ratio: ratio between the probability of a negative test result given the presence of the disease and the probability of a negative test result given the absence of the disease, i.e.
= False negative rate / True negative rate = (1-Sensitivity) / Specificity

Positive predictive value: probability that the disease is present when the test is positive.

Negative predictive value: probability that the disease is not present when the test is negative.

Sensitivity, specificity, positive and negative predictive value as well as disease prevalence are expressed as percentages.